Bidirectional myofiber transition through altering the photobiomodulation condition.

Area of Science:

• Muscle physiology
• Regenerative medicine
• Biomedical engineering

Background:

• Muscular atrophy is a significant clinical challenge with varying pathological characteristics.
• The role and function of distinct muscle stem cell populations in atrophy are not fully understood.
• Satellite cells (SCs) are crucial for muscle regeneration and repair.

Purpose of the Study:

• To investigate the differential effects of photobiomodulation (PBM) on fast and slow muscle stem cells.
• To explore PBM's potential in altering skeletal muscle composition and neuromuscular junctions.
• To assess PBM's synergistic effects with exercise in combating muscle atrophy.

Main Methods:

• Isolation of Pax7-positive satellite cells (SCs) from fast (tibia anterior) and slow (soleus) muscles.
• Application of photobiomodulation (PBM), also known as low-level laser irradiation (LLLI), with varying exposure durations.
• Analysis of SC proliferation, myofiber composition, and neuromuscular junction alterations.
• Evaluation of PBM combined with muscle exercise.

Main Results:

• Demonstrated distinct optimal PBM exposure durations for promoting proliferation of fast and slow muscle SCs.
• Achieved bidirectional shifts in myofiber composition (slow-to-fast or fast-to-slow) and neuromuscular junction constitution via PBM.
• Observed a synergistic effect of PBM with muscle exercise, enhancing myofiber size.

Conclusions:

• Identified at least two distinct populations of Pax7-positive SCs with differential sensitivities to PBM.
• PBM can modulate skeletal muscle composition and neuromuscular junctions, potentially strengthening contractility.
• PBM represents a promising therapeutic strategy for muscular atrophy, adaptable through controlled irradiation conditions.